Two US military planes have flown over a disputed part of the East China Sea, defying China's new 'air defence zone'.

The unarmed B-52 aircraft took off from Guam on Monday on a flight previously scheduled as part of a routine exercise in the area, the defence officials said.

"Last night we conducted a training exercise that was long-planned. It involved two aircraft flying from Guam and returning to Guam," Pentagon spokesman Colonel Steven Warren said.

He said the planes conducted operations near a group of islands claimed by both Japan and China.

"We have continued to follow our normal procedures, which include not filing flight plans, not radioing ahead and not registering our frequencies," he said.

No flight plan was submitted beforehand to the Chinese and the mission went ahead "without incident," with the two aircraft spending "less than an hour" in the unilaterally-declared Air Defence Identification Zone (ADIZ), he added.

There was no Chinese response, Colonel Warren said.

Over the weekend, China announced the expanded 'air defence zone', amid growing territorial tensions with Japan.

'Unnecessarily inflammatory'

The US says the dispute over the islands must be resolved diplomatically.

"The policy announced by the Chinese over the weekend is unnecessarily inflammatory," White House spokesman Josh Earnest said.

"These are the kinds of differences that should not be addressed with threats or inflammatory language, but rather can and should be resolved diplomatically."

Along with Japan and the US, Australia also questioned Beijing's announcement.

Australia's Foreign Minister Julie Bishop said the timing and the manner of China's announcement were unhelpful and will not contribute to regional stability.

"Australia has made clear its opposition to any coercive or unilateral actions to change the status quo in the East China Sea," she said in a statement.

The Chinese embassy says the ambassador welcomed the opportunity to present China's position, and the move is in line with the UN Charter and international law.

Ambassador Ma Zhaoxu has asked Australia not to take sides in the conflict and "take concrete measures uphold China-Australia strategic relationship."

Under the rules declared by Beijing, aircraft are expected to provide a flight plan, clearly mark their nationality and maintain two-way radio communication to allow them to respond to identification inquiries from Chinese authorities.

Its expanded defence zone also includes waters claimed by Taiwan and South Korea, which also have both expressed their displeasure at Beijing's move.

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